The Seismic Gap Theory in geology has been somewhat controversial, even though some of its predictions appear to be rational, ie that movement of a tectonic fault along a plate boundary should be more or less continuous unless that slippage is blocked, in which case it is liable to sudden slippage (large earthquake) if strain starts to build.
The seismic gap hypothesis states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries. One of the earliest and clearest applications of the seismic gap theory to earthquake forecasting was by McCann et al. (1979), who postulated zones of high, medium, and low seismic potential around the Pacific rim.
A paper by Kagan and Jackson (1991) “Seismic Gap Hypothesis: Ten Years After” appeared to find that the Seismic Gap Hypothesis did not match reality:
In the 10 years since , there have been over 40 large (M ≥ 7.0) earthquakes, enough to test statistically the earlier forecast. We also analyze another forecast of long-term earthquake risk, that by Kelleher et al. (1973). The hypothesis of increased earthquake potential after a long quiet period can be rejected with a large confidence. The data suggest that, contrary to these forecasts, places of recent earthquake activity have larger than usual seismic hazard, whereas the segments of the circum-Pacific belt with no large earthquakes in recent decades have remained relatively quiet. The “clustering” of earthquake times does not contradict the plate tectonic model, which constrains only the long-term average slip rate, not the regularity of earthquakes.
But in certain places, the long term slippage of a tectonic fault is more or less continuous in terms of low level earthquakes, unless for some reason, the slippage is impeded and the strain on the fault builds until a catastrophic earthquake occurs. This appears to have happened in the recent Christchurch (Lyttleton) earthquakes.
From Wolfram Alpha, the earthquakes above magnitude 3 for the last 30 years show a continuous range of small earthquakes and then a sudden year-long gap of no earthquakes at all followed by several large earthquakes that devastated Christchurch and the surrounding area.
The gap before the Lyttleton earthquake was noted by Warwick Hughes, but his graph was a little ideosyncratic.
The more recent series of devastating earthquakes off the east coast of Japan also show a short gap of a few months before the big ones happened:
Clearly the Seismic Gap Hypothesis has some life left in it, after all.